Use a plain text editor to open [ Interface > AddOns > nUI > Layouts > Default > HUDLayouts > {hud mode} > nUI_HUDSkin_{hud mode}_{unit id}.lua ] where {hud mode} is the HUD mode you use (PlayerTarget, HealthPower, etc.) and {unit id} is the unit you want the mouseover to work for {Player, Target, etc.)

Locate the ["Aura"] section that for the "harm" auras and change "clickable = false" to "clickable = true" and save the file then do a '/nui rl' -- you should be all set.

Note that because auras are now protected frames, I cannot show/hide them, I can only make them transparent. That means that even when the aura is not visible, it is still on the screen and therefore interacting with your mouse. That will mean you cannot click in the field of play anywhere an aura is positioned... which is why the mouseover tooltips are current disabled by default. However, as long as that doesn't bother you, it will work.

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What people don't get is that I am, ultimately, an artist at heart. My brush has two colors, 1 and 0, and my canvas is made of silicon.